\begin{figure}[htbp]
\centering
\subfloat[`左脚清明`]{
  \label{fig:improved_subfig_a}
  \begin{minipage}[t]{60pt}
    \centering
    \includegraphics{left.pdf}
  \end{minipage}
}
\subfloat[`右脚反复`]{
  \label{fig:improved_subfig_b}
  \begin{minipage}[t]{60pt}
    \centering
    \includegraphics{right.pdf}
  \end{minipage}
}
\caption{`反清复明`}
\label{fig:improved_subfig}
\end{figure}
